Process of vulcanizing rubber and products obtained thereby



Patented Jan. 10, 1939 NITED STATES PROCESS OF VULOANIZING RUBBER AND PRODUCTS OBTAINED THEREBY Robert L. Sibley, Nitro, W. Va, assignor, by mcsne assignments, to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing. Application October 23, 1930, Serial No. 490,814

5 Claims.

This invention relates to the vulcanization of rubber by an improved process, wherein there is of compounds and Table II gives the results when diphenylguanidine benzoate is so used.

Table I Modulus of elasg f ticity in lbs/in. at Tensile Ultlmate Time of cure 9 elongations oflbs/1n. on ati n,

gum at break percent hydrochloride 15 minutes at 10# steam per square inch None 85 133 349 1140 990 0. 1 l 84 151 422 1845 980 0. 2 94 185 440 1970 980 20 minutes at l# steam per square inch None 108 201 556 1870 930 0. 1 97 200 675 2095 910 0. 2 139 241 740 2185 910 30 minutes at 10# steam per square inch None 131 300 952 2465 875 0. 1 165 312 1070 2640 875 0. 2 157 328 1090 2810 880 1% hours at 20?; steam per square inch None 315 963 3400 4200 750 0. 1 366 1040 3620 4320 750 0. 2 336 1095 3850 4380 745 Table II Modulus of elas- 23"; ticity m lbs/111. at Tensile Ultimate Time of cure g g elongations oflbs./m. elongation,

bemoan, at break percent 15 minutes at 10# steam per square inch None 85 133 349 1140 990 0. 1 93 173 440 1720 980 0. 2 88 173 433 1803 970 20 minutes at 10# steam per square inch None 108 201 556 1870 930 0. 1 133 227 709 2040 910 0. 2 132 236 661 2210 930 30 minutes at 10# steam per square lnch None 131 300 952 2465 875 0. 1 140 311 1183 2650 865 0. 2 152 322 1045 2665 875 1% hours at 20# steam per square inch None 315 963 3400 4260 750 0. 1 316 1000 3580 4250 745 0. 2 326 1055 3710 4200 735 employed a member of a preferred class of com pounds which improve the action of the accelerator used in the vulcanization process and with them form a mixed accelerator. The preferred class of compounds employed in the manner hereinafter described comprises salts of a guanidine and derivatives thereof.

As examples showing the use of the preferred class of compounds, a rubber mix was prepared in the well known manner comprising 100 parts of pale crepe rubber, 5 parts of zinc oxide, 3 parts of sulfur, 0.5 part of the crotonaldehyde derivative of the reaction product of mercaptobenzothiazole and hexamethylene-tetramine, 0.5 part of diphenylguanidine, and 0.1 and/or 0.2 part of a compound of the preferred class of activators as hereinafter mentioned. The mix was then vulcanized by heating under various pressures and for various periods of time. The cured stock Was then tested to determine its modulus and tensile strength under various degrees of elongation. The results of the tests of s the rubber composition thus described are set forth in the following tables. Table I gives the results when diphenylguanidine hydrochloride is employed as an example of the preferred class It is readily apparent from the data set forth in Tables I and II that the preferred class of materials possesses highly desirable activation properties.

As examples of the use of the preferred class of compounds, showing retarding effect in the shorter timed and lower steam pressure cures and activation in the longer timed and higher steam pressure cures, the following three rubber stocks, designated A, B and "0 were prepared and tested in the manner hereinbefore set forth.

Grotonaldehyde derivative of the reaction product of mercaptobenzothiazole and hexamethylene-tetramme Diphenylguanidine Diphenylguanidine phthalate Diph enylguanidine acetate The results of the tests upon the above described rubber stocks after curing for various periods of time and under various steam pressures are given in Table III, which shows by comparison the Table III comprising 100 parts of pale crepe rubber, parts of zinc oxide, 3 parts of sulfur, 1 part of stearic acid, 0.4 part of the acetaldehyde derivative of .the reaction product of para-para-diamino-diphenyl-methane and mercaptobenzothiazole, and

Modulus of elasticity in on" Steam lbs/in. at elongations of- Tensile Ultimate minuts pressure Stock lbs/in. elongation,

' in lbs/in. at. brea percent A 54 98 188 1195 1090 15 B Oure insufficient for test.

0 DOI- I A 98 l 144 I 398 l 1718 I 990 20... 10 B Cure ir sufficient for test.

a 117 223 818 2360 s95 30 10 B Cure insufficient for test.

A 98 182 592 2120 935 10 20 B N 3 test ma de.

A w 182 382 1450 3040 830 20 20 B 90 139 334 1060 920 A V 315 968 3920 4175 710 90 20 B 285 810 3260 4290 755 A comparison of the results given in Table III shows that the preferred class of materials as for example diphenylguanidine phthalate and di- 1 phenylguanidine acetate, not only activate the curing process in the longer timed and higher steam pressure cures, but also greatly retard the cure in the shorter timed and lower steam pressure cures. This retardation of cure at the lower temperatures is a highly desirable property, as scorching or vulcanizing on the mixing rolls is thereby substantially prevented.

As further examples of the use of the preferred class of materials, a rubber mix was prepared 0.6 part of the preferred class of materials. The results of the tests upon the above rubber stock after curing are given in the following tables. Table IV gives the results of tests of the cured rubber product in which diphenylguanidine phthalate was incorporated in the above described rubber stock prior to the vulcanization thereof. Table V gives the results of tests obtained when diphenylguanadine hydrochloride was employed in the manner described above, and Table VI sets forth the results obtained when diphenylguanidine acetate was employed in the above identified stocks in the manner described.

Table IV MIR-$11111? 0% ollasticizzy in S111. a eon alons f g Tensile Ultimate Time of cure lbs/in. elongation,

at break percent 20 minutes at 10# steam per square inch 89 178 534 2080 970 25 minutes at l0# steam per square inch--- 131 266 871 2285 890 30 m nutes at 10# steam per square inch--- 141 334 1155 2835 860 minutes at steam per square inch.-. 159 396 1405 3260 885 30 minutes at 20# steam per square inch--. 253 771 2758 4310 800 45 minutes at 20# steam per square inch--- 323 1110 3788 4685 760 1 hour at 20# steam per square inch 418 1510 4610 4610 700 1}}? hours at 20# steam per square inch 418 1510 4610 4610 700 2 ours at 20# steam per square inch 441 1590 4455 675 Table V Mlrdulus of; ellasticiity in sm. a con a ions l g Tensile Ultimate Time of cure lbs/in. elongation,

at break percent 300% 500% 700% 20 minutes at 10# steam per square inch 128 255 S35 2650 925 25 mlnutes at 10# steam per square inch 148 322 1205 2905 875 30 minutes at 10# steam per square inch 163 378 1450 3675 875 15 minutes at 20# steam per square inch 156 400 1570 3190 860 30 mmutes at 20# steam per square mch 255 741 2830 4290 795 45 rnlnutes at 20# steam per square lnch 326 1115 3945 4510 745 1 hour at 20# steam per square inch" 411 1525 4728 4775 705 1% hours at 20# steam per square me 411 1525 4728 4775 705 2 hours at 204! steam per square inch- 459 1718 4945 685 Table VI Mlldvi lus oellasticlgy in s in. a e on a 1011s g Tensile Ultimate Tune of cure lbs/in. elongatlon,

\ I at break percent 300% 500% 700% 20 minutes at 10 pounds steam per square inch.. 76 133 346 1375 985 25 minutes at 10 pounds steam per square nch 92 180 512 2080 975 30 minutes at 10 pounds steam per square inch 104 226 721 2328 955 15 minutes at 20 pounds steam per square inch 110 228 754 2375 955 30 minutes at 20 pounds steam per square inch- 174 396 1472 3315 870 45 minutes at 20 pounds steam per square inch- 215 560 2015 3780 830 1 hour at 20 pounds steam per square inch... 261 732 2655 3850 775 1% hours at 20 pounds steam per square inch. 261 732 2655 3850 775 2 hours at 20 pounds steam per square inch 279 776 2780 3990 770 A stock identical with that employed in the test given in Tables IV, V and VI with the exception The results of the tests upon the above rubber stock after curing are given in Table VII.

Table VII Mfi) 671111: of; ellasticiity in sm.aeonarons 12- g Tensile Ultnnate Time of cure lbs/in. elongatmn,

at break percent 300% 500% 700% 20 minutes at 10# steam per square inch D d not cute 30 minutes at 10# steam per square inch. 290 890 2350 2955 790 10 mlnutes at 20# steam per square 111011. 200 578 1550 2285 825 15 mlnutes at 20# steam per square inch 301 925 2470 2835 750 30 minutes at 20# steam per square inch 361 1140 2960 3500 700 45 minutes at 20# steam per square inch. 404 1250 3185 3595 735 60 minutes at 20# steam per square inch--. 434 1280 3360 3515 720 that diphenylguanidine was substituted for the diphenylguanidine salts, on curing for 20 minutes at 10# steam pressure, gave a tensile at break of 2780 lbs. /in. and an ultimate elongation of 920%. The foregoing tests given in Tables IV, V and VI show that the preferred class: of activating materials, when employed in the rubber stock described, retards or delays the curing action during the early stages of the vulcanization, process but permits the accelerator to exert substantially its normal effect at full cure. In fact, the materials appear to first serve as retarders and later as activators, at least, the full activating effect of the materials is not produced during the early stages of the cure.

As a further example of the use of the preferred class of materials, a rubber stock was prepared comprising the following:

Parts Pale crepe rubber Sulfur 2 Zinc oxide 5 XVhitiug 30 Lithopone 20 Palm oil 2 The reaction product of 2 mols mercaptobenzothiazole and 1 mol pht halyl chloride Diphenyl guanidine .1 Diphenyl guanidine phthalate .399

It is readily apparent from the results set forth in Table VII that in the presence of one of the preferred class of materials, for example, diphenylguanidi 1e phthalate, the vulcanization is retarded in the early period of the cures, but this retarding effect is not continued in the longer cures and the cures at the higher steam pressures.

As a further example of the use of the preferrecl class of materials, a rubber stock was prepared comprising the following:

The results of the tests upon the above rubber stock after curing are given in Table VIII.

Table VIII Modulus of elasticity in lbs/in. at elongations Tensile Intimate Time of cure lbs/in. elongation,

at break percent 300% 500% 700% 20 minutes at 10# steam per square inch. Did not cure 30 minutes at 10# steam per square inc 177 l 496 l 1, 315 I 805 10 minutes at 20# steam per square me Not fit for test 15 minutes at 20# steam per square Inc 215 665 1, 850 2, 450 800 30 m nutes at 20# steam per square me 306 960 2, 600 3, 360 780 m nutes at 20# steam per square inch 374 1,165 3,050 3, 420 750 60 minutes at 20;; steam per square inch 412 l, 265 3, 185 3, 340 730 It is apparent from the results set forth in Table VIII that in this example also, as in pre- The results 'of the tests upon the above rubber stocks after curing are given in Table IX.

Table IX Cute Steam Modulus of Elasticity in Tensile Ultimate mjnutgs pressure Stock lbs/i11 at elongations oi lbs/in elongation,

in lbs/in. 300% 500% at break percent 30 10 A. 322 1108 1553 590 V B 325 880 939 520 vious examples cited, the presence of one of the preferred class'of materials, for example, diphenylguanidine phthalate, retards the vulcanization process in the shorter timed cures, but the vulcanization of the compounded rubber stock wherein the preferred class of materials is incorporated is, not retarded on the longer heating period and at the higher steam pressure cures.

As further examples of the use of the preferred class of materials, two rubber stocks, designated A" and B, were prepared and tested for comparison, stock A comprising diphenylguanidine as an activator and stock B comprising diphenylguanidine acetate in its stead as one ,of the preferred class of materials. The rubber stocks here referred to comprised the following ingreclients:

A comparison of the results given in Table IX gives further proof that the presence of one of the preferred class of materials, for example, diphenylguanidine acetate, retards the vulcanization in the shorter timed and lower steam pressure cures, but activates the vulcanization in the longer timed and higher steam pressure cures.

The results hereinbefore set forth show that a vulcanized rubber product of particularly high quality is obtained by employing the preferred substances in a rubber stock, of vulcanizing characteristics.

Other salts of guanidines than those hereinbefore set forth may be employed in the manner described. Thus, the phthalate, hydrochloride, acetate, and similar salts of di-ortho-tolyl-guanidine, dixylylguanidines, triphenylguanidines, and analogous compounds may be employed in the vulcanization of rubber in a manner analogous to that hereinbefore set forth.

This invention is not restricted to the use of the particular compounds given in the disclosure as examples, nor is it restricted to the use of the preferred class of compounds in the particular rubber mixes herein described. The invention is limited only by the claims attached hereto as part of the present specification.

What is claimed is:

l. The process of vulcanizing rubber which comprises heating a mixture of rubber and sulfur in the presence of diphenylguanidine phthalate and in addition thereto a mercaptothiazole accelerator.

2. The process of vulcanizing rubber which comprises heating a mixture of rubber and sulfur in the presence of an accelerator containing diphenylguanidine phthalate and a reaction product of substantially two molecular proportions of mercaptobenzothiazole and substantially one molecular proportion of phthalyl chloride.

3. The process of vulcanizing rubber which comprises heating rubber and sulphur in the presence of a mercapto aryl thiazole accelerator and the diphenyl guanidine neutral salt of phthalic acid.

4. The process of initially retarding the accelerating action of a mercaptothiazole accelerator and later activating the accelerating action thereof which comprises heating rubber and sulphur in the presence of a mercaptothiazole accelerator and the diphenyl guanidine neutral salt of phthalic acid.

5. The process of vulcanizing rubber which comprises heating a mixture of rubber and sulfur in the presence of a thiazyl sulphide accelerator and in addition thereto an aryl substituted guanicline salt of an aromatic carboxylic acid, said acid being one of a group consisting of phthalic and benzoic acids. 

